The present invention relates to a seat reclining apparatus.
In a conventional seat reclining apparatus which is disclosed in Japanese Utility Model Laid-open Print No. Hei 2(1990)-141228, as shown in FIG. 4, a pair of lower arms 51 (only one is shown) are set to serve for supporting a common seat-cushion (not shown), and each lower arm 51 is secured, via a rivet 55, with a lower plate 53 provided with an outer gear 53a. A pair of upper arms 52 (only one is shown) are set to support a seat-back (not shown), and each upper arm 52 is secured, via a rivet 56, with an upper plate 54 having an inner gear 54a which is in meshing engagement with the outer gear 53a. The lower plate 53 and the upper plate 54 are fitted therein with a common shaft 57 in such a manner that the lower plate 53 and the upper plate 54 are rotatably mounted on a centric portion 57a and an eccentric portion 57b of the shaft 57, respectively. In addition, the upper plate 54 is interposed between the lower arm 51 and the lower plate 53 which is secured thereto by the rivet 55 so that a left portion of the upper plate is held by a right portion of the lower arm 51.
However, a gap between a portion at which the lower arm 51 is secured with the lower plate 53 and a plane at which the lower arm 51 holds the upper plate 54 becomes large, which leads to a fear that the lower arm 51 is subject to deform in the direction of X upon application of a force in the same direction. Thus, a clearance may generate between the lower arm 51 and the upper plate 54, whereby an axial play is generated at the upper plate 54, the meshing engagement between the inner gear 54a and the outer gear 53a becomes imperfect, and mechanical strength therebetween becomes poor. In the light of the fact that the upper plate 54 is held by the lower arm 51, in order to prevent the deformation of the lower arm 51 in the direction of X, the lower arm 51 is compelled to be pressed onto the upper plate 54 entirely. This means that a high precise press is required for holding the upper plate 54 at the lower arm 51.